Graphene Micro-Supercapacitors

Project Overview

The electronic devices we use in our everyday life utilize two different types of electrical sources in order to operate: batteries and capacitors. A battery stores a fair amount of energy but is slow to charge and discharge (low power density). A capacitor can charge and discharge very rapidly (high power density) but stores a very small amount of energy. A supercapacitor combines the best of both by storing a large amount of energy while also being able to charge and discharge very rapidly.

A capacitor is often constructed with two layers of conducting foil separated by a paper-thin layer of insulator. The capacity of such a device is proportional to the area of the foil A and inversely proportional to the insulator thickness t, C∝A/t. A supercapacitor has an atomic scale insulator thickness given by the solvation layer surrounding an ion in an electrolyte, and a large surface area. Supercapacitors on the order of 100 - 103 Farads are now commercially available and approach the energy density of batteries while still offering fast charge and discharge rates.

The authors of the Nature paper below, El-Kady and Kaner, have provided a video introduction to graphene based supercapacitors.

Project Goals

Short Term Goals

Create graphene micro-supercapacitor material using the methods outlined by El-Kady and Kaner.

Conduct a series of tests on how to maximize the amount of charge stored within each graphene micro-supercapacitor.

Long Term Goals

Design an apparatus that can hold many graphene micro-supercapcitors in an efficient and usable way for use in application.

Experiment with powering small mobile devices (ie. a flash light, a watch, a cellphone).

Relevant Publications

El-Kady and Kaner demonstrate a scalable fabrication of graphene micro-supercapacitors over large areas by direct laser writing on graphite oxide ﬁlms. More than 100 micro-supercapacitors can be produced on a single disc in 30 min or less. The devices are built on ﬂexible substrates for ﬂexible electronics and on-chip uses. Remarkably, miniaturizing the devices to the microscale results in enhanced charge-storage capacity and rate capability. These microsupercapacitors demonstrate a power density of ~200 W cm-3, which is among the highest values achieved for any supercapacitor.

The conventional method for the preparation of graphitic oxide is time consuming and hazardous. Hummers and Offema have developed a rapid, relatively safe method for preparing graphitic oxide from graphite in what is essentially an anhydrous mixture of sulfuric acid, sodium nitrate and potassium permanganate.